This invention relates to a compact and portable detection device for specific chemical compounds, such as hazardous chemicals or illegal drugs, for example heroin, cocaine or marijuana. The portable device can be conveniently carried by an individual, is extremely sensitive to the compound being detected, and is minimally affected by potential interfering substances.
The device of the present invention is based upon the use of fiber optic spectroscopy. Sensors to detect light emitted from an optical fiber can be constructed that are sensitive, compact, readily portable, and require a minimum of training for their use. The preferred process of the invention relies upon a biological system, and optical and electronic components to monitor a decrease in fluorescence when a subject molecule (such as a drug) displaces a fluorescently-tagged drug derivative (antigen) from an antibody specific for that drug.
Fluorescence occurs when an atom or molecule emits visible radiation when passing from a higher to a lower electronic state. The term is restricted to phenomena in which the time interval between absorption and emission of energy is relatively short (10.sup.-8 to 10.sup.-3 second), thus distinguishing fluorescence from phosphorescence, wherein the time interval may extend to several hours. Fluorescent materials may be liquid or solid, organic or inorganic. Fluorescent crystals such as zinc or cadmium sulfide are used in lamp tubes, television screens, scintillation counters, and similar devices. Fluorescent dyes are used for labeling molecules in biochemical research.
Illicit drug traffic throughout the world has been steadily rising. It is estimated that in 1985, over 150 metric tons of cocaine and approximately 6 metric tons of heroin were smuggled into the United States alone. It is also estimated that less than 4% of these drugs were detected and confiscated as they crossed our borders even though current interdiction methodology has improved. During 1987, 27 thousand pounds of drugs were confiscated; during 1988, 38 thousand pounds; and in the first few months of 1989, 10 thousand pounds. However, methods and techniques for smuggling drugs have also improved, and it is a certainty that only a small percentage of the drugs entering this country are confiscated. It is speculated that a high percentage of the drugs entering this country are concealed in enclosed spaces, such as cargo containers. On average, approximately 15 manhours are required to thoroughly search a cargo container, so that less than 3% of the 8 million cargo containers entering the United States each year are inspected. Because of the vast number of cargo containers and enclosed boxes of every description, a method for rapid inspection and detection is required
One reason for the low rate of drug interdiction is the lack of adequate instrumentation available to field agents. Most of the instruments currently available, such as mass spectrometers and gas chromatographs are not portable, require 100/220V power, and must be operated by well-trained technicians. Therefore, instrumentation is needed that is readily portable, operable with a minimum of training, capable of detecting the compounds of interest at extremely low concentration, minimally affected by interfering substances, rugged, and completely user friendly.
While the apparatus and process of the present invention are initially intended to detect illegal drugs, the invention is equally applicable for detection of a wide range of chemical compounds, limited only by the biological and tagging procedures set forth below. Therefore, the invention should not be considered as limited solely to the detection of drugs. For example, the methods described herein can be used in business or industrial environments to detect the presence of certain hazardous chemicals likely to be found in such environments.
Cocaine and heroin vapors in the air are typically detected with mass spectrometry and GC-MS. However, the "stickiness" of the drug molecules and their extremely low vapor pressures present measurement problems. The drug molecules tend to adhere to tubing walls instead of entering the detection chamber. Because of the drugs' low vapor pressures, concentration is required for detection. This typically consists of passing a large volume of air through tubing or a filtering system and then liberating the attached drug molecules with heat.
Another method of detecting illegal drugs is described in U.S. Pat. No. 4,353,886, issued Oct. 12, 1982. This patent discloses the vapor deposition of indium onto a glass slide which is then coated with an antibody specific for a given drug. Since indium functions as a Lewis acid (an electron acceptor) the non-antigen binding end of the antibody, with a high amine concentration, preferentially attaches to the indium metal. The antigen binding end is therefore free to combine with any drug (or antigen) molecules in the air. After exposure to the drug, the test plate can be read either by visual observation of cloudiness or by fluorescence measurement. Drugs with a vapor pressure of 1.times.10.sup.-9 Torr can be detected with a one- to two-minute exposure of the test plate.